Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $85.75   13.421%   $97.2585   $97.26   $97.25   $97.30  
  Purchase #2 $187.44   9.577%   $205.3911   $205.39   $205.40   $205.40  
  Purchase #3 $225.80   8.653%   $245.3385   $245.34   $245.35   $245.30  
  Purchase #4 $236.68   3.839%   $245.7661   $245.77   $245.75   $245.80  
  Purchase #5 $55.63   6.573%   $59.2866   $59.29   $59.30   $59.30  
  Purchase #6 $111.41   6.291%   $118.4188   $118.42   $118.40   $118.40  
  Purchase #7 $25.59   12.576%   $28.8082   $28.81   $28.80   $28.80  
  7 purchase totals = $928.30       $1,000.2678   $1,000.28   $1,000.25   $1,000.30